High-gain multibeam gnss antenna

ABSTRACT

A multibeam Radio Frequency (RF) lens antenna is designed as a receiver for Global Navigation Satellite System (GNSS) applications, such as GPS (Global Positioning System), Galileo, GLONASS, COMPASS, and others. The RF lens and plurality of associated feed elements and receiver circuits combine to form a plurality of resulting high-gain relatively narrow beams that, taken together, allow reception of signals from GNSS satellites over the entire upper hemisphere. Any kind of RF lens can be used, where the lens can be of homogeneous or inhomogeneous, dielectric or metamaterial/metasurface construction. The benefit of this approach to build a GNSS receiver over existing alternatives is increased gain and decreased noise at each receiver, which improves the signal to noise ratio (SNR) and improves the accuracy and reliability of the position and time measurements, while also reducing the impact of, and sensitivity to, interference, jamming, and spoofing signals. The approaches described in this patent can be combined with existing signal processing and accuracy improvement methods (such as Real-Time Kinematic (RTK), Precise-Point Positioning (PPP), and Differential GPS (DEPS)) for further benefits. This system has applications within the surveying, maritime, land mobility, aerospace, and government positioning market areas.

RELATED APPLICATION

This application claims the benefit of priority of U.S. Application Ser.No. 62/953,311 filed on Dec. 24, 2019, the content of which is reliedupon and incorporated herein by reference in its entirety.

BACKGROUND

Achieving higher levels of position and time accuracy in less time hasbenefits in many industries and applications. Many of these approachesrely on new and improved signal processing techniques that extract themaximum possible amount of information from the weak and noisy signal.However, even better would be improving the quality of the signalitself, since the signal processing methods would all continue to addadditional value.

The antenna is an important part of a Global Navigation Satellite System(GNSS) receiver, as the antenna determines how much of the signal ispicked up and forwarded to the signal processing system. Many antennasare used for GNSS reception, but the vast majority are static, with afixed radiation pattern. Improvements to the antennas focus onoptimizing the radiation pattern to cover as much of the upperhemisphere as possible while minimizing the radiation pattern directedtowards the ground or terrestrial sources of interference.

The Global Positioning System (GPS), as the first of the satellite-basedpositioning systems, has had many antenna designs created to fit oneniche or another. Currently, antennas for GNSS fall into one of threegeneral categories: Low-cost Fixed Radiation Pattern Antennas (FRPA);High-performance FRPA; and Controlled Radiation Pattern Antennas (CRPA).

Low-cost FRPA focus on optimizing the radiation pattern of a singleradiating element, and will generally be low-cost and physicallycompact, but with low to moderate gain and angular performance. Thelargest concern with these antennas is mitigating interference fromterrestrial sources near the horizon and backlobes, so balancing thegain in the upper hemisphere with sufficient rejection in the lowerhemisphere on a small ground plane is often a challenge. These are themost common form of GNSS receiver antennas. Some of these antennas areintegrated directly into the integrated circuit packaging or printedcircuit board for more convenience but poorer performance.

High-performance FRPA use higher-quality materials and construction oradditional structures and geometry to improve the patterns and phasecenter stability and reduce the sensitivity to interference of the basicsingle-element antennas. Often using the same patch or helix base, thehigh-performance antennas can improve performance with amplifiers,larger ground planes, structured ground planes (such as multilevel chokerings), or absorbing structures to control the backlobes, sidelobes, andboresight radiation patterns. These antennas are less common and areused primarily in high-precision applications such as surveying andprecision timekeeping. The key benefit of this class of antenna isreduced sensitivity to reflected and multipath signals from theenvironment.

CRPA use multiple methods to allow dynamic changes to the hardware andsignal processing system to alter the radiation patterns in response toreal-time conditions. The purpose of changing the radiation pattern isto increase resilience to intentional or unintentional jamming orspoofing by placing a null in the radiation pattern at or near theangular source of the interference. Some CRPA systems use explicitphased array approaches with multiple receivers that combine the signalsfrom number of feed elements (each of which might be similar to one ofthe ordinary FRPA mentioned above), and others use a single antenna butchange the state of switches or excitation points to tilt, rotate, orotherwise alter the radiation pattern. These systems are almostexclusively used for military applications where jamming, spoofing, andinterference is of strong concern.

The CRPA described to date have a number of benefits over moreconventional FRPA, but are still limited in their achievableperformance. Phased array implementations are typically limited to asmall number of elements, and are typically used to perform nullplacement to isolate interferers rather than improve signal reception ingeneral. The processing required to combine the signals from thedifferent elements also drives the cost and complexity of the antenna.

This present system and method describes a new form of GNSS antenna thatimproves the signal strength and reduces the noise levels at thereceiver by passively segmenting the sky into separate regions, reducingthe error contribution and measurement uncertainty, and reducing thetime required to a position measurement of a desired accuracy.

SUMMARY

The present system and method relate to the receiving of signalstransmitted from satellites and ground infrastructure for determiningposition and time synchronized to one or more of the satellitepositioning constellations (GPS, Galileo, GLONASS, etc.). Although thereare some differences between the operation of the different systems, thesame principles apply to all. A set of transmitters (in space or on theground) with accurate, synchronized clocks broadcast messages includingthe time of transmission and the position of the transmitter. Receiverson the ground independently collect and decode the messages frommultiple transmitters and use the information to compute a time andposition estimate based on triangulation methods. The accuracy that canbe obtained with this approach is limited by position uncertainties ofthe satellites, the wavelength, and other properties of the transmittedsignal, uncertainties as to the propagation characteristics of theatmosphere, the presence of unwanted noise and interference, and lowsignal strengths at the receiver. Even very poor reception can bemitigated, however, by gathering measurements over an extended periodand averaging the results to help remove the impact of the time-varyingerror sources (although this does not assist with systemic errors).

Improving the signal strength with improved antennas is a key method ofimproving the accuracy of GNSS receivers for many applications,including (but not limited to) property and construction surveying,automated agricultural, mining, and construction equipment, navigation,self-driving vehicles, and defense and military vehicles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a lens antenna unit.

FIG. 2 shows a lens with two feed positions showing multiple beams.

FIG. 3 shows a jammer signal or interference that is shown to beisolated by a single (or multiple) beam(s).

FIG. 4 shows multiple lenses employed as an array for additionaldirectivity diversity.

FIG. 5 is a block diagram of signal path from the lens to datacombining.

FIGS. 6 a, 6 b show two possibilities for the RF front-end, asuperheterodyne and a direct-digital receiver (SDR).

FIG. 7 is a flow chart for signal processing.

DETAILED DESCRIPTION

In describing the illustrative, non-limiting embodiments of the systemand method illustrated in the drawings, specific terminology will beresorted to for the sake of clarity. However, the system and methoddisclosed is not intended to be limited to the specific terms soselected, and it is to be understood that each specific term includesall technical equivalents that operate in a similar manner to accomplisha similar purpose. Several embodiments of the system and method aredescribed for illustrative purposes, it being understood that thedisclosure may be embodied in other forms not specifically shown in thedrawings.

Multibeam Lens antennas offer advantages across many applications buthave previously not been utilized for GNSS receivers. New advances inlens antenna architecture now permit smaller size, wider scan range, andmultiple simultaneous beams across the field of view. This disclosuredescribes receiver architectures that utilize improved lenses to offersubstantial advantages compared to the state of the art.

Turning to the drawings, FIGS. 1, 2 show a lens antenna 101 having alens 103 and a plurality of feeds 105, each with an associated receiverfront end 117, and the signals from all of the feeds 105 and receivers117 are combined and digitized by a digitizer such as in a combiner 119.Each feed, when enabled, produces a corresponding beam 111 from thesingle shared lens antenna 101. in a direction set by the position ofthe feed 105 (and the phase center 107 of each feed) relative to thefocal point 113 of the lens 103. In this way, multiple beams share thesame aperture, and multiple beam directions can come from the samephysical region. The high gain of the lens compared to the gain of thefeeds without the lens leads to each beam covering only a subset of thesky, while the set of all of the beams allows signals from the entireupper hemisphere to be received. The gain of the resulting beam 111depends on the size and physical characteristics of the lens. The gainof the beam decreases in general with larger scan angles from boresight.Each beam is characterized by a distinct effective phase center 109,which is the physical point from which the energy of the beam appears tobe emanating, and is affected by the lens and feed design. Stability ofthe phase center of each beam across frequency and coverage range of thebeam is highly important for accurate positioning. Multiple feeds can beenabled simultaneously. In this case, enabling feeds 105 a and 105 bsimultaneously produce separate beams 111 a and 111 b in differentdirections from the lens antenna 101.

The radio characteristics of the lens antenna 101 are defined by thecombination of the lens 103 and the feed 105. For GNSS receiverapplications, GNSS satellite signals strike the lens 111 and then arebent as they encounter the lens 103 and are refracted by the dielectricmaterial from which the lens is constructed. Multiple feeds at differentlateral locations behind the lens relative to the focal point of thelens produce multiple beams whose angles are determined by the lensdesign and position of the feed element 105.

A lens is any diffractive or refractive structure that concentrates orspreads energy. This includes the simple homogeneous dielectric lensesthat are used for optical wavelengths and gather or spread light usingthe shape of the surface. The same principle applies at RF wavelengths.However, significantly greater performance (as measured in apertureefficiency and realized gain across a wide frequency range and field ofview) can be achieved for a lens-based antenna when using more advancedlenses, such as metamaterial, metasurface, gradient index, orDiffractive Optical (DO) element lenses. The described system can useany suitable lens, though in the lens configurations described in U.S.Published Application No. 2018/0183152 permit considerably smaller lenssize for a given wavelength of operation. U.S. Pat. No. 10,116,051, theentire contents of which are hereby incorporated by reference, offerparticularly strong advantages, including wide scanning range, broadbandoperation, high efficiency and reduced size.

Any kind of RF radiator can be used as the feed 105, but particularfeeds of interest will typically include patch antennas or waveguideantennas. This system is described as using patch antennas as the feedelement 105 due to their many convenient properties (simple manufacture,compact, and planar), but can be implemented with other feed elements aswell.

The primary benefits of a lens antenna for GNSS purposes is their highgain and multibeam properties. Any multiple beam antenna for GNSS willinherently have superior capabilities for mitigating multipath,interference, and jamming signals. Existing multibeam antennas for GNSSeither use multiple distinct apertures tilted at different angles tocover the field of view or use a phased array with digital or analogbeamforming techniques to steer beams at the desired satellites and ornulls at targeted sources of interference. The lens antenna proposedhere has the advantage of generating multiple beams in differentdirections from the same aperture area, defined by the lens 103, butdoes not require the power-hungry beamforming circuitry, since each feednaturally acts to cover a specified region of the sky through thepassive beamforming of the lens while still making use of the entireantenna aperture. A lens 103 with planar bottom surface andapproximately planar focal surface permits the feed elements 105 to bemounted on a single planar structure with inherently lower mutualcoupling and easier manufacturing than existing multibeam antennas.

In the lens antenna, signals arriving from different directions will bepropagated through the lens to different corresponding points below thelens. For example, referring to FIG. 2 , a satellite signal coming fromone direction (Beam 1) 111 a will propagate and be received by feedantenna 1 located at feed position 1105 a. Simultaneously, a signalarriving from the direction of (Beam 2) 111 b will propagate to feedposition 2 where feed antenna 2 is located 105 b.

FIG. 3 shows a GNSS lens antenna 101 listening to satellites 301 in thepresence of a jammer or other interferer 325. The signals from thedifferent satellites are received by different beams 111 a, 111 b, 111c, 111 d associated with separate feeds 105 a, 105 b, 105 c, 105 d andreceivers 117 a, 117 b, 117 c, 117 d.

With this configuration, where the lens antenna uses individual feeds105 a, 105 b, 105 c to listen to satellites 301 a, 301 b, 301 c, thejammer 325 (which might be intentional or unintentional) only impactsthe received signal of a single beam 111 d and feed 105 d, and allowsthe remaining feeds 105 a, 105 b, 105 c to continue operating. Comparedto a phased array where all of the feeds in the antenna are usedsimultaneously to generate each beam, the same jammer 325 would beincident on all of the feeds and would potentially degrade the receivedsignal from all of the beams. If the jammer were strong enough tosaturate the front-end amplifier, then the entire antenna could in thatcase be effectively disabled.

However, in the multibeam lens antenna, a strong enough jammer 325 coulddisable a single receiver beam, but the remaining beams would continueto operate. This functionality can also be described as spatialfiltering, since each beam is associated with a region, cone, or subsetof the sky. Since the signals from each of the feeds 105 are processedindependently, interference on one beam that prevents error-freereception of signals from one satellite will not impact reception ofsignals in different beams.

FIG. 4 shows lenses 103 of multiple lens antennas 101 placed in aconformal shape 401 that can further extend the coverage range andperformance compared to a single lens. The multiple antennas 101 in thearray 401 would be configured to function cooperatively to form multiplebeams and increase overall system gain and therefore received signallevels.

The lens-based GNSS antenna forms only one component of the system. Thelens antenna is coupled with analog and digital signal processingcircuitry to receive and interpret the signals from the satellites andcompute the location and orientation of the antenna.

FIG. 5 shows the circuit architecture for the lens GNSS lens antenna101, which contains the feeds 105 and receiver front-ends 117 and signalprocessing circuitry 119, 515, jointly forming a GNSS receiver. Thefront-end receiver 117 is connected to the output of the feed 105, andhas filters 505, low-noise amplifiers 507, and optionally mixers 508.Depending on the feed polarization, there can be either one or two ofeach component per feed to account for either dual-linearly-polarizedfeeds or single-circularly polarized feeds. The resulting signals fromall feeds are then passed to the signal processing circuitry 119, wherethe signals are then sampled to digital bitstreams by the AID converters509, and combined with the signals from the other receiver front ends117 a by the multiplexer/combiner 511, which may sum the signalsexplicitly, or only combine the signals into a single bitstream fortransport by the wired or wireless link to the signal processor 515. Thelens 103, feeds 105, receiver front-ends 117, and combiner 119 arecollocated as part of the antenna 101 by the requirement of minimizingloss and cabling complexity. The digital signal processing (DSP)processor 515 then forms the GNSS receiver as conventionally defined,that converts the satellite signals from the antenna into pseudo-rangemeasurements and then a computed position. As in many conventional GNSSantennas, the first low-noise amplifiers and other front-end signalconditioning circuitry 117, 119 must be collocated with the antennaitself to minimize conductive losses and other distortions. Once thesignal has been amplified and potentially digitized, a longer cable orother wired or wireless data path 513 can be used to run to an externalprocessor 515 without loss of signal integrity.

There are several hardware complexities that accompany multibeamarchitectures. There are N beams 111 associated with N feed elements105, and thus also N receiver front ends 117, including the filters 505,LNAs 507, and possible down converters 508.

For this multibeam configuration, the phase centers 109 of each beam 111will not, in general, be in the same location, either across scan anglesor between beams. Because the phase center of the beam 111 is criticalfor computing positions based on signals from different satellites, anydifferences in the phase centers 199 from each beam 111 must becorrected or compensated for in the digital processor 515 before thesignals may be used to compute a location estimate. The direction ofarrival of each signal can be estimated with a high degree of accuracyby comparing the relative magnitude and time offset of the same signalreceived from adjacent feeds.

FIGS. 6 a, 6 b . show two example implementations for the RF front-end117 and combiner 119 implementations, namely a superheterodyne receiverarchitecture 601 in FIG. 6 a that includes a downconverting mixer 508before the AID converter 509, and a direct digital receiver architecture603 in FIG. 6 b that does not include a mixer. Both implementations arecompatible with the disclosed system, and the decision between them maybe based on component availability, cost, frequency responses, andfiltering requirements. Both components have different advantages, butultimately have the same interface to the signal processor 515 of adigital bitstream. Recent improvements in cost, power consumption, andsampling rate of Analog to Digital converters (ADC) allow for a directsampling receiver, which reduces the analog circuitry required.

FIG. 7 shows a block diagram that illustrates the digital processingsequence 701 taking place in the digital signal processor 515. Thedigital processing functions can be performed by a processing devicesuch as general-purpose processors, digital signal processors, orvirtualized processors and signal processing circuits performed on anFPGA or other reconfigurable circuit. A control process will coordinateand command the subsidiary processes for each beam. In one embodiment,the steps 701 (including steps 703-727) are performed by the digitalprocessor 515 (FIG. 5 ).

For each beam, the processing steps 703 (which include steps 705-717)are performed. Within the steps 703, the process begins with thedigitized signal from the corresponding beam 111. A power detector 705has an algorithm that is first used to detect and/or characterize themagnitude of the received signal. A comparator 707 then compares thesignal strength against a predetermined threshold based on normaloperation. If the power levels exceed the threshold, then jamming orother interference has been detected 709, and the signal from thecorresponding beam is ignored.

If the power level does not exceed the threshold, then the signal ispassed through a GNNS signal detection & de-spreading operation 711,which produces as its output signal level estimates in the form ofcarrier power to noise plus interference power (C/N+I) ratios and thedetected and extracted signals themselves. A separate output isavailable for each extracted satellite signal detected as present ineach beam, along with the corresponding C/N+I. The signal detection andde-spreading is performed in the same way as is done in ordinary GNSSreceivers, with the distinction that the operation is repeatedseparately for each of the beams 111 of the multi-beam antenna 101.Signals from an individual satellite are received in one or more beams,and multiple beams will have different satellites present. The benefitsof receiving fewer signals in each beam are that the beams have moregain to increase the received carrier power, and there would be fewernoise and interference sources in the reduced field of view of a singlebeam compared to the entire sky, thus reducing the interference term.Both effects have the effect of increasing the C/N+I ratio and thusimproving the capability of the antenna and related receiver tosuccessfully receive satellite signals.

A comparator 713 evaluates the C/N+I ratio for all of the detected andextracted signals, and determines whether any of the signals exceed apredetermined threshold of normal operation and represents a jamming orother interference signal 709. If the threshold is exceeded, it isdetermined that the signal is a jamming or interference signal, and thesignal is ignored, step 709.

If the threshold is not exceeded, a further comparator 715 evaluates thedirection of arrival of each detected signal coarsely from theindividual beam coverage area and compares this measured direction ofarrival with the expected satellite location based on the current timeand the known satellite ephemeris. Mismatches between the expected andactual direction of arrival of the signals over and above a predefinedthreshold indicate the presence of a spoofing signal 719, and the signalis ignored by the further processing steps.

If there are no mismatches, the signals are corrected 717 for the phasecenter of the current feed 105 and beam 111. Additional correctionscommon to all GNSS receivers, including correction for atmosphericconditions, ephemeral data, those obtained from DGPS, RTK, PPP or otherGNSS error correction mechanisms, and other conditions are also appliedby 717.

The signals received and processed in parallel from all of the feeds(i.e., all of the steps 703 conducted for each beam) are then combinedinto one data set to be processed together in the remaining steps. Thelist of extracted signals across all of the beams are de-duplicated instep 721, by the processor 515. Cases where the signals from the samesatellite are received and extracted by multiple beams are removed andreplaced either by an amalgamated signal having the weighted and delayedsum of the signals from each of the beams, or more simply by thestrongest of the individual signals. In cases where the separatepolarizations (left and right-hand circularly polarized) are receivedand processed independently from the feeds 105 through to the processor515, signals in the same beam but opposite polarization can be used todetect incidence of multipath or ground reflections, which ordinarilyresult in significant errors in the computed locations of a GNSSreceiver.

Explicit detection and measurement of the cross-polarized signals can beused to either exclude the signals subject to multipath and reflectionsfrom consideration, or with the support of multipath propagation modelscan be used to strengthen and correct the primary signal, once thepolarization and time offset are applied to make corrections accordingto the multi-path propagation models. After the de-duplication andsignal combination steps are complete, only a single copy of each signalis retained and used to compute pseudo-range data for each extractedsatellite signal. The set of duplicate signals for each satellite fromdifferent beams removed during the de-duplication process are used tomeasure (with more precision than 715) the direction of arrival of thesatellite signal by examining the relative magnitude and delay (phaseand time) between of signals received from the same satellite intomultiple beams. The measured direction of arrival is then compared 723to the satellite ephemeris data to determine whether there are anymismatches between a received signal and the expected satellitelocation, and mismatches above a predetermined threshold result in thesignal being ignored as a possible spoofing signal 719.

Finally, the remaining signals (that have not been eliminated due todetected jamming 709 or spoofing 719) are used by the processor 515 inthe location calculation algorithm 725 to compute the current estimatedlocation of the antenna 727.

The majority of GNSS satellites are in non-geostationary orbits (NGSO),such as LEO, EO, HEO, etc., and so move relative to the ground. Merelyfrom the satellite motion, or from the movement of the antenna 101,which satellite signals are received by which beams will change overtime, and there will be discrete periods of time (handoff or handover)in which the same signal is received by multiple beams. This case ishandled by the multipath combination process 721 that monitors forcopies of the same signal from multiple feeds and operates to generate asingle signal from two or more (potentially weak) signals. The C/N+I ofeach of the signals can be used by the multipath combiner 721 to decidewhich to use and which to ignore, or how to combine the signals. As theC/N+I ratio decreases in one beam 111 a and increases in an adjacentbeam 111 b, a soft handoff may be implemented by combining by summationwith time-delay to maximize the correlation of the two signals andgradually shifting the demodulated signal response from one beam toanother. The alternative method is a hard handoff, where the output ofthe combiner 721 is chosen as the single strongest signal.

If the GNSS receiver/antenna is kinematic, another level of complexityexists. The antenna is changing position and orientation with time, andso signals received at different times, from the same or differentsatellites, are received while the antenna is in different locations.This is solved by using Gyroscopes and Accelerometers to form anInertial Motion Unit (IMU) that inertially tracks the relative movementof the terminal accurately over short time scales (1-120 sec). In thesecases, successive measurements of satellite pseudo-range are correctedin the location calculations 725. In such cases, the “place” in the PRNcode that has locked the de-spreader is “remembered” by the tracking PLLand switched between or among multiple correlators for constanttracking.

The capability of the antenna for use in kinematic applications can beextended by tracking the orientation as well as the location of theterminal, and correlating the orientation of the terminal against therelative directions of the satellites. As the terminal and thesatellites move and reorient relative to each other, the beam(s)receiving the signals from a particular satellite will change over time.If each of the detection processes 711 for each beam are completelyindependent, then a single changing between feeds would requirere-detection of the satellite and synchronization in the new beam.Instead, the solution is to share the loop tracking parameters andoffsets between beams for each satellite in view, so that a new signalreceived into a neighboring beam can start processing based on theexisting locked beam, while still allowing the PLL for each beam toshift relative to each other to account for multipath, reflections, andphase center differences.

An additional implementation can change what is done with detectedjamming and spoofed signals, rather than ignoring the signals outright.Very strong jamming or interference can affect the signals from multipleadjacent beams, not only the single beam directed most closely. Adetected interference or spoofing signal can then be used by aninterference cancelation system to cancel or subtract the undesiredsignal(s) from the desired signals received by neighboring feeds. Thiscan also be interpreted as null-placement or beamforming; by subtractingsignals received in one beam from a neighboring beam with an appropriatemagnitude and phase offset, the effective radiation pattern of theneighbor beam can be modified to reduce sensitivity to the signal fromthe undesired direction.

Considerable improvement in gain is realized compared toomni-directional antennas since narrow beams also exhibit highdirectivity. The lens antenna is also very efficient and thus littlegain is sacrificed compared to directivity. This increases the C/N+Iratios for all satellite signals received and thus improves the two mostimportant GNSS receiver parameters: location accuracy and reduced timefor an accurate location measurement. When a jamming signal is present,a single beam isotropic antenna can be rendered useless as the frontend, particularly when the LNA is overloaded. This is also the case inphased arrays, since all antenna elements and their associated LNAs musthandle ALL signals incident on the array. With multibeam antennas, thebeams themselves reject signals off-beam, therefore the only beams thatare overloaded are the beams that include the direction(s) of thejammer(s).

Lenses can be produced from multiple materials and constructions, etc.(metamaterial, dielectric, metasurface, Fresnel, transformation optics,stepped gradient, homogeneous, GRIN, etc.). The lenses for implementinga lens-based GNSS antenna can be built by 3D printing, injectionmolding, machining, casting, thermoforming, shaped foams, multilayerstacks of plastic with holes cut into it, or other methods. The lensesmay be spherical, as in the Luneburg lens, or non-spherical orsubstantially planar. The substantially planar or non-spherical case isdesirable as it leads to a simpler and more cost-effective feedarchitecture (allowing for planar printed circuit board implementations,rather than something more complex for a spherical lens).

An extension of the GNSS antenna is to include bidirectionalcommunications (transmit and receive capability) within the neighboringL-hand communications channels, in addition to the GNSS receptioncapability within a single lens antenna. This case where single antennaunit can provide both GNSS navigation & time services as well asbidirectional satellite communications is beneficial for platforms withlimited surface area for antennas. This implementation would includebroader-bandwidth receive amplifiers, transmit amplifiers, as well asfilters with higher isolation to enable operation of the transceiverwhile maintaining lock on the GNSS satellites. The benefits described ofthe system for the GNSS receiver application would also exist for theL-band SATCOM transceiver antenna for use with services such as Iridiumor BGAN, namely, higher gain, reduced sensitivity to interference andspoofing, and reduced interference between satellite signals due tobeing received in multiple beams simultaneously.

There are several possible form factors for the lens-based GNSS antennaand receiver. In most implementations, the front ends 117 and combiner119 will be co-located with the antenna. The balance of the rest of thesystem (including the DSP processor 515) can also be contained withinthe same structure thus creating a “single piece” multibeam antenna andreceiver system. Alternatively, especially where weight is a majorfactor, the digitized outputs of the antenna can be combined 119 andsent either through a cable or a wireless connection 513 to the digitalsignal processor. In some applications ever greater system distributionmay be optimum.

A key innovation of the described radio frequency lens-based GNSSantenna is the use of the lens to generate multiple disjoint beamsacross the field of view of the antenna, and then process the extractedsignals from each beam separately. Across all of the beams, the signalsfrom all satellites within line-of-sight are received. Thisconfiguration is in contrast to conventional phased array-based GNSSantennas that use either null-placement or beam-tracking methods toattenuate identified interferes or to follow individual satellites. Theuse of fixed beams to cover the sky increases the antenna gain andtherefore the signal level, reduces sky noise (and discrete interferencesources), and does not require beamforming or steering to be performed,simplifying the antenna. Advancements in signal processing capabilityand falling cost and power requirements make this architecture feasible,since it does require more signal processing resources to accomplish.Other high-gain or array-based GNSS antennas combine the receivedsignals together after beamforming, which eliminates the benefit ofreceiving the individually lower-noise signals from different sectors ofthe sky. This system allows reception from satellites close to thehorizon, while still allowing for mitigation of ground-level jamming andspoofing sources, in comparison to conventional high-availabilityapproaches that instead rely on reducing antenna gain at the horizon andlimiting the field of view of the antenna.

Any signal processing approach that leads to improved performance(including, but not limited to time-domain signal cancellation,kinematics post-processing, position integration) that can be applied toanother GNSS antenna can he applied to this one.

Applications

Since the antenna described will offer the possibility of highperformance, nearly every application that demands high performance canutilize this technology. Among them are: Cadastral surveying,Construction surveying and machine control, Mine surveying, Agriculturesurveying and machine control, Autonomous vehicle (includingautomobiles), Marine surveying, Ship navigation, Aircraft navigation,Transportation, Law Enforcement, Base station, and Time references. Theantenna supports multiple specific frequencies selected from L1, L3, L5for GPS, GLONASS, Galileo and GNSS standards.

The foregoing description and drawings should be considered asillustrative only of the principles of the disclosed embodiments. Thesystem and method may be configured in a variety of shapes and sizes andis not intended to be limited by the embodiment. Numerous applicationsof the systems disclosed will readily occur to those skilled in the art.Therefore, it is not desired to limit the disclosure to the specificexamples disclosed or the exact construction and operation shown anddescribed. Rather, all suitable modifications and equivalents may beresorted to, falling within the scope of the disclosure.

1-16. (canceled)
 17. A satellite receiver, comprising: a plurality offeeds, wherein three or more of the plurality of feeds are configured toreceive signals from respective three or more satellites simultaneously;a lens shared by the plurality of feeds, wherein the signals received bythe three or more of the plurality of feeds propagate through the lens;and a processor coupled to the plurality of feeds and configured todetermine a time and a position of the satellite receiver by processingthe signals received by the three or more of the plurality of feeds,wherein processing the signals received by the three or more of theplurality of feeds comprises compensating for a difference in phasecenter associated with each of the three or more of the plurality offeeds and, subsequently, performing triangulation using the signalsreceived by the three or more of the plurality of feeds.
 18. Thesatellite receiver according to claim 17, wherein a surface of the lensclosest to the plurality of feeds is a planar surface.
 19. The satellitereceiver according to claim 18, wherein a focal surface of the lens isapproximately planar.
 20. The satellite receiver according to claim 19,wherein the plurality of feed elements is mounted on a single planarstructure.
 21. The satellite receiver according to claim 17, wherein theprocessor is configured to receive signals received by four or more ofthe plurality of feeds, and a first feed and a second feed among thefour or more of the plurality of feeds receive signals from a samesatellite.
 22. The satellite receiver according to claim 21, wherein thefirst feed is adjacent to the second feed, and the processor isconfigured to compare relative magnitude and time offset of a samesignal from the same satellite received at both the first feed and thesecond feed to estimate a direction of arrival of the same signal. 23.The satellite receiver according to claim 21, wherein, for each of thesignals received from the same satellite by the first feed and thesecond feed, the processor is configured to use a stronger one of thesignals for the triangulation.
 24. The satellite receiver according toclaim 21, wherein, for each of the signals received from the samesatellite by the first feed and the second feed, the processor isconfigured to use, for performing the triangulation, an amalgamatedsignal having a weighted and delayed sum of the signal received at thefirst feed and the signal received at the second feed.
 25. The receiveraccording to claim 17, wherein the processor is configured to determinea measured direction of arrival of each of the signals received by eachof the three or more of the plurality of feeds.
 26. The satellitereceiver according to claim 25, wherein the processor is configured toobtain ephemeris data indicating a trajectory of each of the three ormore satellites and to determine an expected direction of arrival ofeach of the signals received by each of the three or more of theplurality of feeds based on the ephemeris data.
 27. The satellitereceiver according to claim 26, wherein the processor is configured toidentify a presence of a spoofing signal based on a comparison of themeasured direction of arrival to the expected direction of arrival ofeach of the signals received by each of the three or more of theplurality of feeds.
 28. A satellite receiver, comprising: a lens havinga curved front surface; a plurality of feeds disposed behind the lenseach having a respective phase center, wherein the plurality of feedscomprises three feeds configured to receive satellite signals fromrespective satellites via the lens; and a processor configured toperform a triangulation operation to determine a time and a location ofthe satellite receiver using the satellite signals received by the threefeeds after compensating for the respective phase centers of the threefeeds.
 29. The satellite receiver according to claim 28, wherein thelens has a substantially flat back surface proximate the plurality offeeds.
 30. The satellite receiver according to 29, wherein the lens is aplano convex lens.
 31. The satellite receiver according to claim 29,wherein the processor is remote from the lens and plurality of feeds.32. The satellite receiver according to claim 29, wherein the threefeeds are configured to receive the satellite signals from respectivesatellites simultaneously.
 33. A multi-beam Global Navigation SatelliteSystem (GNNS) antenna system, comprising: a two-dimensional arrangementof a plurality of lenses, including a first lens; a plurality of feedsets disposed under respective lenses of the plurality of lenses,including a first feed set disposed under the first lens, wherein thefirst feed set comprises three or more feeds configured to receivesignals from three or more respective satellites simultaneously; and aprocessor coupled to the plurality of feed sets and configured todetermine a time and a position of the multi-beam GNSS antenna system atleast in part by processing the signals received by the three or morefeeds, wherein processing the signals received by the three or morefeeds comprises compensating for a difference in phase center associatedwith each of the three or more feeds and subsequently performingtriangulation using the signals received by the three or more feeds. 34.The multi-beam GNNS antenna system of claim 33, further comprising adirect digital receiver coupled to a first feed of the three or morefeeds.
 35. The multi-beam GNNS antenna system of claim 33, furthercomprising a super heterodyne received coupled to a first feed of thethree or more feeds.
 36. The multi-beam GNNS antenna system of claim 33,wherein the plurality of feed sets disposed under the respective lensesof the plurality of lenses are configured to operate in cooperation toproduce multiple beams.